Whether milling road surfaces, removing pavement as a first step in replacing same, providing trenching operations or long wall and other mining operations, various combinations of bit assemblies have been utilized to remove material from the terra firma. The end point where material removing equipment contacts the surface of the pavement to be removed is traditionally comprised of a bit assembly that may include bits having a pointed forward end, the bits either mounted on or made an integral part of a bit holder and base blocks in which the base of the bit/bit holder is mounted. The base blocks may be mounted on either an endless chain, a chain/plate system, or a rotatable drum.
Presently, the most common use of such a bit assembly for road milling use is found on a rotatable drum wherein a plurality of such assemblies are mounted, either in V-shape or in spiral form around the outside of the drum. An improvement in such assemblies by applicant is found in U.S. Pat. Nos. 6,371,567, 6,585,326 and RE 44,690, wherein the bit holder or middle piece of the bit assembly is no longer required to be retained on the base block by a threaded shank with a nut therein holding the bit holder on the base block. This improvement by the present applicant included a hollow shank comprising a distal end that is axially slotted, wherein the shank may be driven into a bore in the base block and the distal end of the shank is compressed radially with a sufficient radial force between the bit holder shank and the base block bore to maintain the bit holder mounted on the base block during use.
While such bit assemblies have traditionally been made of a hardened material, such as tungsten carbide, lately, either man-made polycrystalline diamond or industrial diamond material have been utilized to form layers or coatings on tungsten carbide base inserts to provide longer lasting points of contact between the material removing machinery and the pavement, substrate, or other earth material.
These diamond layered or coated bit tip inserts have a substantially longer in-service life for certain pavement removing operations and do not have to be rotatably mounted in a bit holder body in order to provide substantial length of service between replacements. Such material removing end contact products may be termed bits, bit/bit holders, picks, or the like, although all perform the same function of removing material as desired.
When used in road milling or road removal equipment, the bit assemblies are usually positioned in a spiral or V-shape fashion, across a generally cylindrical drum. The spiral or V-shape configuration allows the bit assemblies to be staggered across the drum in closer center-to-center axial bit tip orientation, and allows the loosened material to flow toward the center of the drum to exit the drum housing onto the disposal conveyor. Such heretofore known bit assemblies have included separable bits and bit holders or unitary bit/bit holders with the holder comprising an upper body portion and a hollow slotted shank. The shank has a length approximating 2-½ inches which is compressed radially into a base block bore of similar length. While such staggered V-shape or spiral configurations allow the bit tips to be positioned closer to each other axially along the axis of the drum, the present configuration, with about 2-½ inches long bit holder shanks, crowds the rear access of the holder adjacent the rear of such closely positioned base blocks. This is especially made worse in so-called “double hit” configurations with twice as many rows of such assemblies on each drum.
A need has developed for an improved bit assembly, or parts thereof, that provides greater access to the rear of base blocks for greater ease of removability of bit assemblies therefrom, especially broken assemblies, when such replacement is desired.